The present invention relates to improvements in trucks for railroad vehicles, especially locomotives. More particularly, the invention relates to improved bearing surfaces for those portions of the trucks which are slidably engaged to enable the wheels and the body of the vehicle to move relative to each other in a generally vertical direction.
The truck upon which the vehicle is supported comprises two side frames tied together by a transverse member called a bolster. One type of truck commonly used for locomotives is referred to as a pedestal truck. The pedestals are part of the side frames and are formed in inverted U-shaped sections that horizontally position and hold a journal box to move essentially vertically in relationship to the truck. The two projections that comprise the U of the pedestal are called the pedestal legs and the space between them the jaw. The jaw is closed at the bottom when the journal is inserted by means of a pedestal tie bar. In this manner, the journal box is held positioned in vertical sliding relationship with the truck. As the locomotive body is supported by the bolster and side frames, vertical movement between the locomotive body and the journal box, journal and wheels is permitted.
Considerable wear takes place at the interface between the pedestal and the journal box. Wear plates are attached to both the pedestal legs and journal boxes to reduce wear and protect the underlying parts. The wear plates attached to the pedestal legs are often referred to as pedestal liners and are the subject of the present invention. Qriginally the pedestal liners were made of steel, but more recently they have been made from nylon.
A pedestal liner now in use is produced as a monolithic nylon casting and is produced by known injection molding techniques. The castings are considerably more expensive to produce than injection molded parts, and further this monolithic casting has minimal shock absorbing properties. No spacing washers are employed, and when the coast pedestal liner is installed, the nylon will cold flow due to excess compressive forces causing it to move away from the pedestal leg. This results in relatively poor fit when the pedestal liner is attached to the pedestal leg, as there is a space of about one-sixteenth of an inch between the pedestal liner and the pedestal leg which causes extra wear and results in a shorter working life for the pedestal liner. It is believed impact abrasion occurs on the surface of the liner, leading to increased clearance and subsequent failure.
U.S. Pat. No. 3,554,618 to Ditzler et al discloses a two piece pedestal liner assembly. Although the pedestal liner assembly is produced in two pieces, the assembly has minimal shock absorbing properties since there is only one piece in the wear surface area. No spacing washers are disclosed, and the problems of poor fit discussed above are applicable to this pedestal liner.